agar

Agar, also called agar-agar, is a complex gelatinous product prepared from the algaeGracilaria and Gelidium. Its powder dissolves in hot water,
the solution forming a gel on cooling. It is
used as a thickening agent or emulsifier in foods; as an adhesive;
and as a medium for growing bacteria, mold, yeast, and other microorganisms; as a medium
for tissue culture; and as a gel for electrophoresis.
See also gum.